A methodology to obtain accurate potential energy Functions for diatomic systems: mathematical point of view

The mathematics used in physical chemistry has changed greatly in the past forty years and it will certainly continue to change more quickly. Theoretical chemists and physicists must have an acquaintance with abstract mathematics if they are to keep up with their field, as the mathematical language in which it is expressed changes. Thinking about it, in this article, we want to show some of the most important concepts of Mathematical Analysis involved in obtaining analytical functions to represent the potential energy interaction for diatomic systems. A basic guide for the construction of a potential based on Dunham's coefficients and an example of a new potential obtained from this methodology is also presented

A methodology to obtain accurate potential energy Functions for diatomic systems: mathematical point of view

The mathematics used in physical chemistry has changed greatly in the past forty years and it will certainly continue to change more quickly. Theoretical chemists and physicists must have an acquaintance with abstract mathematics if they are to keep up with their field, as the mathematical language in which it is expressed changes. Thinking about it, in this article, we want to show some of the most important concepts of Mathematical Analysis involved in obtaining analytical functions to represent the potential energy interaction for diatomic systems. A basic guide for the construction of a potential based on Dunham's coefficients and an example of a new potential obtained from this methodology is also presented

CASPT2 Study of the Potential Energy Surface of the HSO(2) System

The importance of the HSO(2) system in atmospheric and combustion chemistry has motivated several works dedicated to the study of associated structures and chemical reactions. Nevertheless controversy still exists in connection with the reaction SH + O(2) -> H + SO(2) and also related to the role of the HSOO isomers in the potential energy surface (PES). Here we report high-level ab initio calculation for the electronic ground state of the HSO(2) system. Energetic, geometric, and frequency properties for the major stationary states of the PES are reported at the same level of calculations:,CASPT2/aug-cc-pV(T+d)Z. This study introduces three new stationary points (two saddle points and one minimum). These structures allow the connection of the skewed HSOOs and the HSO(2) minima defining new reaction paths for SH + O(2) -> H + SO(2) and SH + O(2) -> OH + SO. In addition, the location of the HSOO isomers in the reaction pathways have been clarified.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqFAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Connection between the Upper and Lower Energy Regions of the Potential Energy Surface of the Ground Electronic State of the HSO₂ System

The importance of the HSO₂ system in atmospheric and combustion chemistry has motivated several works dedicated to the study of associated structures and chemical reactions. Nevertheless, controversy still exists about a possible connection between the upper and lower energy regions of the potential energy surface (PES) for the ground electronic state of the system. Very recently, a path to connect these regions was proposed based on studies at the CASPT2/aug-cc-pV­(T+d)­Z level of calculation but the small energy difference between some of the transitions states along that path suggested the necessity of calculations at a higher level of theory. In the present work, we report a CCSD­(T)/aug-cc-pV­(T+d)­Z study of the stationary states associated to the proposed connection path, including assessment of the most reliable complete basis set (CBS) extrapolation scheme for the system. Among the new features, the present calculations show that there are no structures corresponding to the HSO₂(b) minimum and the TS3 saddle point obtained at the CASPT2 level and that the connection path between the upper and lower energy regions of the PES for the ground electronic state involves only one transition state and most probably more than one electronic state

Coupled-Cluster Study of the Lower Energy Region of the Ground Electronic State of the HSO₂ Potential Energy Surface

This work reports CCSD­(T)/aug-cc-pV­(T+d)­Z ab initio calculations for the lower energy region of the ground electronic state of the HSO₂ system. Optimized geometries, total energies, zero-point vibrational energies, frequencies, complete basis set extrapolations, and reaction paths are reported at the same level of calculation. The connection of the two minima (synperiplanar HOSO and HSO₂) with the dissociation limit H + SO₂ through the van der Waals minimum H···SO₂ was established. An important quantitative discrepancy with previous works is the fact that at the present level of calculation the energy difference between transition states connecting the global minimum synperiplanar HOSO to the HSO₂ minimum (TS₅) and to the van der Waals minimum H···SO₂ (TS₆) is negligible, implying that the forward barriers after the synperiplanar HOSO global minimum have practically the same height. This result suggests that these two transition states may be involved in the path of the global minimum toward the exit channel H + SO₂. As a consequence, trajectories for the OH + SO collisions could evolve through the well formed by the HSO₂ minimum, therefore opening two competitive channels for the OH + SO → H + SO₂ reaction, a fact never reported in trajectory calculations